Spermine enhances the activity of anti-tuberculosis drugs

The discovery of molecules that could shorten the treatment period of tuberculosis (TB) holds the promise of improving the current regimen. Polyamines are organic polycationic alkylamines found in millimolar concentrations in all living cells. Spermine (Spm) is a polyamine that was shown (more than 70 years ago) to be toxic to Mycobacterium tuberculosis (M.tb). In this study, we used various biochemical assays to assess the mechanism of action of Spm. Furthermore, using various drug susceptibility testing methods, we investigated the ability of Spm to enhance the activity of first-line TB drugs, isoniazid (INH) and rifampicin (RIF), as well as second-line TB drugs, para-aminosalicylic acid (PAS) and bedaquiline (BDQ). Our findings revealed that at toxic concentrations, Spm induced the formation of reactive oxygen species (ROS), a reaction that was influenced by the pH and the iron concentration of the media. Furthermore, the generation of ROS by Spm was associated with increased ferric iron and NADP levels. Moreover, the ROS produced by Spm synergized with the ROS generated by the lipophilic peroxide cumene hydroperoxide (CuOOH), as well as with the ROS generated by RIF and PAS, while enhancing their antimycobacterial activity. Additionally, we found that Spm enhanced the combined activity of INH and RIF against M.tb. Lastly, Spm was also able to enhance the activity of BDQ due to another mechanism of action. This study provides data and findings that would fuel future studies on the suitability of Spm as a potential adjunct TB therapy. The enhanced antimycobacterial activity of TB drugs in combination with Spm could offer promising new avenues for improving TB treatment outcomes.